2, 2&#39;-ethylene-bis



2,2'-ETHYLENE-BIS(6-TERTIARYBUTYL-PARA- CRESOL) Josef Pikl, Glasshoro,N. 3., assignor to E. I. du Pont de Nemours and Company, Wilmington,Del., :1 corpora tion of Delaware No Drawing. Application April 17,1953, Serial No. 349,563

1 Claim. (Cl. 260-619) This invention relates to new compounds of thebenzene series, and more particularly to the preparation of 2,2-ethylenebis(6-tertiary butyl para-cresol) which has been found to be ofparticular value as an anti-oxidant, and especially as anon-discoloring, odorless anti-oxidant for elastomers.

Although a variety of effective anti-oxidants, such as the diarylamines,are available for rubber and other elastomers when the color developedby the anti-oxidant on aging is not objectionable, non-discoloringcompounds suitable for use in colorless, white, or light-colored stocksand at the same time sufliciently effective as anti-oxidants arediflicult to obtain. Simple phenols, such as para-hydroxydiphenyl, havebeen used and have more recently been supplemented by dihydric phenolswhich contain the diphenylmethane nucleus, such as 2,2'-ethylidenebis(4,6-dimethylphenol) and 2,2-methylene bis(4- methyl-6-tertiary butylphenol). It has been found that the effectiveness of compounds of thistype as anti-oxidants varies greatly, in a way not understood. Therelative positions of the hydroxyl groups, the size, structure andposition of substituting alkyl groups, all seem to have an influence,but in each case the eifect cannot be predicted. Noindiscoloringanti-oxidants which are odorless and which otherwise do not impartundesirable properties to elastorners are needed by the industry.

It is therefore an object of this invention to produce a new chemicalcompound which exhibits desirable properties as an anti-oxidant,particularly for elastomers. It is a further object of the invention toproduce as a new compound 2,2'-ethylene bis(6-tertiary butyl p-cresol).

l have found that 2,2'-ethylene bis(6-tertiary butyl-pcresol) having theformula:

is an effective non-discoloring anti-oxidant for elastomers such asrubber and the synthetic elastomers in general, including thepolychloroprene and polybutadiene elastomers of commerce, and that ithas general utility as an anti-oxidant in other fields whereanti-oxidants of the phenol types are useful.

T o prepare the compound of this invention, 2-tertiary butyl p-cresol isreacted with formaldehyde in a caustic alkalimethanol solution toproduce the Z-tertiary butylfi-methanol p-cresol which in turn isbrominated to give Z-tertiary butyl-6-bromomethyl p-cresol. The lattercompound, after blocking the hydroxyl group such as by forming theacetate, is condensed to produce the 2,2- ethylene bis(6-tertiary butylp-cresol).

2,792,428 Patented May 14, 1 957 The following examples are given toillustrate the preparation of the 2,2'-ethylene bis(6-tertiary butylpcresol) and its use as an anti-oxidant in elastomers.

Example 1 Z-tertiary butyl-p-cresol (492 grams) is dissolved in amixture of 50 cc. of methanol, 60 grams of caustic soda and 340 grams ofwater. To this solution is added 26 7 grams of 35% formaldehyde solutionand the mass is agitated at room temperature for 3 hours. After thereaction is completed water is added and the reaction prod uct dissolvedin petroleum ether and washed with water. On cooling, the Z-tertiarybutyl-6-methylol-p-cresol 'crystallizes from the petroleum ether. It hasa melting point of from to 88 C.

This methylol derivative is treated in benzene solution with gaseoushydrogen bromide in the presence of calcium chloride at roomtemperature. The reaction proceeds as fast as the hydrogen bromide isintroduced, the calcium chloride taking up the Water formed in thereaction. The yield of 2-tertiary-butyl-6-bromomethyl-p-cresol issubstantially quantitative.

The above bromomethyl derivative is reacted for one hour with 1.5 molsof acetic anhydride per mol of the bromomethyl derivative and a fewdrops of concentrated sulfuric acid at 60 to 80 C. and then the productis distilled in high vacuum. The bromomethyl-acetate distills withoutdecomposition at to C. at a pressure of 0.5 mm. of mercury. Analysisshows it has 25.6% bromine (theory: 26.6%).

80 grams of the bromomethyl acetate is dissolved in 200 cc. of anhydrousether and then added to 23 grams of magnesium turnings and 0.2 gram ofanhydrous cuprous chloride. The reaction starts quickly and is held at30 to 33 C. by controlling the addition of the bromomethyl acetate. Thereaction product is decomposed with dilute acid and the acetate grouphydrolyzed by warming for one hour with alcoholic caustic to 80 C. Thereaction product is recovered by acidification and distillation in highvacuum to separate the 2,2-ethylene bis(6-tertiary-butyl-p-cresol) froma lower boiling fraction. The fraction distilling at to C. at a pressureof 0.5 mm. of mercury is 2,2-ethylene bis(6-tertiary butyl-p-cresol).When crystallized from petroleum ether, it forms colorless crystalsmelting at 104 to 106 C. Analysis shows it to have 82.2% carbon and10.18% hydrogen.

Example 2 The 2,2'-ethylene bis(6-tertiary butyl-p-cresol) was tested asa non-discoloring anti-oxidant for rubber in the following white stock,the parts being by weight.

Pale crepe rubber 100 Benzothiazyl disulfide 0.6 Dibutyl ammonium oleate0.5 Zinc oxide 10 Titanium oxide 10 Stearic acid 2 Light process oil 5Sulfur 2.75 Anti-oxidant 1 Test pieces were vulcanized for 30 minutes at40 lbs. steam pressure and were then given an accelerated aging test ina bomb at 70 C. and 300 lbs. pressure of oxygen. The tensile propertieswere determined before aging and at the end of 7 and 14 days. Theresults are reported below in terms of the percentage of the originaltensile strength retained after the varying aging periods.2,2'-methylene' bis(4-methyl-6-tertiary-butyl phenol), a non-discoloringrubber anti-miidant now on the market, was used for comparison.

2,2-ethylene 2,2-metl1ylene Days in Bomb bis(6 tertiarybis-(4-methylbutyl-p-cresol) fi-tertiarybutyl phenol) Percent Percent7...; -2 09 14'; 86 74 The compound of this invention may beincorporated in the elastomer to be protected against oxidation, in anyof the ways commonly used for incorporating solid organic rubberchemicals. Quantities between 0.25% and 2.5% by weight of the elastomerare usually most suitable. The 'compoundmay be used without restrictionwith the usual rubber pigments, fillers, plasticizers, vulcanizingagents and accelerators. It may be used as a non-discoloringanti-oxidant not only with natural rubber but also with the syntheticelastomers, for example, those References Cited in the file of thispatent UNITED STATES PATENTS 2,321,620 Pratt June 15, 1943 2,514,218Albert July 4, 1950 2,514,347 Dunlap July 4, 1950 2,542,688 Johnson etal. Feb. 20, 1951 2,549,118 Newby Apr. 17, 1951 2,653,979 Kropa et alSept. 29, 1953 2,762,787 Goodman et a1. Sept. 11, 1956 OTHER REFERENCESHultsch: Chem. Abstracts, vol. 37 (1943), col. 4059-60 p

